1. Field of the Invention
The present invention relates to an ink for a color filter, a method of fabricating a color filter using the ink, and a color filter fabricated by the method. More particularly, the present invention relates to an ink for a color filter capable of improving uniformity of the color filter, a method of fabricating a color filter using the ink, and a color filter fabricated by the method.
2. Description of the Related Art
A liquid crystal display (“LCD”) has advantages of a smaller size, a lighter weight, and a larger display screen over a conventional cathode ray tube (“CRT”). The development of LCDs has been actively made. Particularly, LCDs have been developed sufficiently to serve as flat displays, and thus, are used as screens for mobile phones, personal digital assistants (“PDAs”), digital cameras and camcorders as well as monitors for desktop computers and large-sized displays. The range of applications for LCDs is increasingly being extended.
An LCD is manufactured by preparing a substrate equipped with a pixel electrode and a switching element, and a substrate equipped with a color layer for implementing colors, a black matrix for dividing red (“R”), green (“G”), and blue (“B”) cells and performing a light-blocking function, and a common transparent electrode (e.g., Indium Tin Oxide) for use in applying a voltage to liquid crystal cells; disposing the two substrates such that the pixel electrode and the common electrode face each other; and injecting liquid crystals into a space between the two substrates. The LCD is a device for displaying an image by applying an electric field between the two electrodes, thereby allowing the electric field to move liquid crystal molecules so that light transmittance can be changed.
The color implementing process of an LCD is performed by controlling transmittance by means of passage of white light emitted from a backlight through liquid crystal cells, and mixing colors of light that has been transmitted through R, G, and B color filters disposed adjacent to one another.
The most general method for use in fabricating a color filter is a pigment dispersion method. The pigment dispersion method is a method of forming R, G, and B color filters by forming a photosensitive resin layer with pigments dispersed therein on a substrate with black matrix (“BM”) patterns formed thereon, and repeatedly performing, typically three times, a photolithography process for forming a single color pattern through light exposure and development.
Since the pigment dispersion method requires formation of individual color filters for expressing respective colors, it has disadvantages in that the process is cumbersome and uses a long processing time. Furthermore, the pigment dispersion method wastes considerable amounts of raw materials (pigments, binders, etc.) since most of the photosensitive resin layer having a specific color, and which has been coated on an entire surface of a substrate, is removed during processing.
In order to overcome such problems and fabricate an inexpensive color filter by a simpler fabrication process, fabricating a color filter using an inkjet printing method is in the spotlight. The inkjet printing method is a method of forming a color filter by coating desired amounts of color inks on pixel openings formed between organic black matrix (BM) patterns. At this time, since the color inks should be coated only on the pixel openings, the organic black matrix serving as boundaries of the color inks is formed to have a high repulsive force against the color inks.
The black matrix patterns are placed at respective boundaries of color layers of the color filter. Therefore, when the color inks are coated on a substrate on which the organic black matrix (BM) patterns are formed, the high repulsive force of the organic black matrix (BM) against the color inks prevents the color inks from being mixed between adjacent pixels, improves uniformity of the pixels, and prevents the color inks from overflowing to adjacent pixels, thereby securing a predetermined error range depending on a coating position and improving a processing margin.
However, as shown in a cross-sectional view of a pixel 10 prepared with a conventional color ink in FIG. 1B, a conventional color ink 13 for a color filter has a high repulsive force against a surface 14 of the aforementioned patterned black matrix (BM) 12 and also has a high repulsive force against a surface 17 of a glass substrate 11 and a wall surface 15 of the black matrix (BM) in a pixel opening 16. Therefore, when color ink 13 is coated on a pixel opening 16 by an inkjet printing method, and because the color ink 13 has a high repulsive forces against the surface 17 of the glass substrate 11, the color ink 13 may not coat the entire surface of the glass substrate 11 in the pixel openings 16, and partially uncoated regions may be produced on the glass substrate 11 (see FIG. 1A). Furthermore, in FIG. 1B since wettability of the color ink to the wall surface of the black matrix (BM) 12 is poor, the color ink 13 is coated with a large curvature 14 on the surface of the ink which can extend onto the glass substrate 11 and thus forms an uneven surface. When the curvature 14 is increased in a color filter, this causes defects such as light leakage (light escaping from around the junction of the pixel and black matrix) and a residual image due to uneven arrangement of liquid crystals.